Debris orbiting around the earth increasingly is a concern to all space operations due to potential collisions with existing or new space vehicles. Low inclination, low orbiting objects (LILO) are of particular threat because current ground detection systems don't adequately address them, either due to the location of the ground detection system or due to the mode of operation of the ground detection system. Since all assets pass through this ‘debris field’ periodically, attention to these objects is paramount. Because of the orbital speeds and the energy involved, an object only 10 cm long could destroy a satellite, while an object only 1 cm could disable a spacecraft. Smaller objects could also cause significant damage to spacecraft, including disabling vital on-board systems.
NASA recently estimated that more than 20,000 objects currently orbiting around Earth are larger than a softball, more than 500,000 objects currently orbiting around Earth are larger than a marble, and that million more objects are currently orbiting around Earth that are so small they cannot be accurately tracked. Of the objects orbiting around Earth, the greatest concentration of orbital debris is thought to be around 800-850 km from Earth, with most objects orbiting within 2000 km from the Earth. This is the Low Earth Orbit (LEO) range.
The number of orbiting objects makes it difficult to catalog and to track the debris. Additionally, the amount of orbital debris is expected to increase over the next few years and decades.
Numerous types of systems exist or are proposed for the purpose of space object detection and characterization. The proposed systems include ground-based radar, ground-based phased array radar, ground-based optical detection, space-based optical detection, space-based IR detection, and space-based radar. Currently, there are three main Space Situational Awareness (SSA) systems. These include the U.S. Space Surveillance Network (SSN), the European Space Agency's (ESA) Space Situation Awareness Program (Space Surveillance and Tracking—SST), and the International Scientific Optical Network (ISON). Additionally, nations interested or active within space exploration, such as Russia, China, Norway, Australia, India, Japan, South Africa and the UK have or plan to have equipment for surveilling space. The Space Data Association (SDA) includes all the major satellite communications companies, which typically utilize data from SSA systems to protect their assets.
The SSN and SST both comprise two main parts: surveillance and tracking. The surveillance segment monitors a large area of the sky (creates a “fence”) and passively waits for objects to pass through that area of the sky (i.e. cross the fence). The tracking segment has a very small field of view and is an active system. Data (orbit parameters) from the surveillance segment are refined by the tracking segment if the rough estimate is accurate enough for the tracker to find it in its small beam. In June of 2014, the U.S. Air Force awarded Lockheed Martin (L M) a $914M contract for a ground-based radar system called “Space Fence”. The Space Fence is an upgrade to the existing SSN and consists of two S-band phased arrays. The Space Fence program is slated to run till 2018 and has a potential value of more than $1.5B over an eight-year period.
Each of the existing or proposed SSA systems has drawbacks. Most drawbacks are related to the limited data acquisition abilities of the systems, the inability of surveillance systems to attain precision orbit parameters of newly detected objects, the lack of 24/7 availability (e.g. ground optical systems), and the system costs and complexity. The principal limitation of all present methods is the perceived need to comprehensively search all space, since an arbitrary object at an arbitrary time could be almost anywhere in the sky. Larger aperture sensors, while providing greater sensitivity, narrow the field of view and enlarge the space to be searched. It would be useful to develop a system and method for detecting and determining the orbit for earth orbiting objects that is relatively simple, that is highly accurate, that limits a search to a portion of available space, and that is able to quickly detect and catalog earth orbiting objects.